I just downloaded an Xcode project, and I get all these errors about "ARC Restrictions." What are these, and how can I remove them?
There are basically two versions of memory management in objective-c. ARC and... well, "Not ARC" :-) You probably downloaded a project, which doesn't use ARC already. Simplest way of resolving your problem is to instruct the compiler to treat your sources as "Not ARC". Explained here.
And here is a good tutorial that should get you started with ARC.
ARC automatically keep track of memory release and retain so you can not release and retain any memory manually.
ARC also doesn't allow any method to be get called at compile time which prototype is not declared in interfaces.
It has also introduced new #autoreleasepool block. so it doesn't not allow older autorelease of an object automatically
However it has allowed dealloc method to be written, but it doesn't allowed [super dealloc] to be get called.
There are much more written about ARC at this blog you can checkt it here
You can covert your project to ARC using xcode in following way.
Go to Edit -> Refactor -> Convert to objective c arc.
However it has some compatibility issue with git repository so it does not convert when .git folders are there in projects. so you will have to remove it first and then convert it. check this link
Related
Hello I am completely new to Apple development
I used this code in my project
https://github.com/vladinecko/accordion-uitableview/tree/master/AccordionTableView
, project releases the memory itself using autorelease
What made me disable the ARC
Because ARC does not allow the use of autorelease
My question is whether to delete the autorelease from the code
And use ARC or i can not do it and I need to have to release the memory for myself
You could leave the code as-is—you can compile some files using ARC and others not, but that’s going to be messy and hard to maintain.
What I’d recommend doing is running Xcode’s ARC-ifying on the code, to get rid of retain and release and autorelease.
In Xcode 5, look under the “Edit” menu for “Refactor”, and select “Convert to ObjC ARC”.
Apparently AccordionTableView does not use ARC, whereas in your project you are using it.
So you have three options
Switch off ARC only for the separate compilation units, which are from AccordionTableView
Adapt the code snippet from AccordionTableView project with ARC guidelines
Switch your own project to not use ARC
First, being new to Objective-C development you need to learn how memory management works. Google for "Apple memory management" and you should find relevant documents.
Before ARC, people did memory management by hand. With ARC, ARC does it for you. The exact same memory management operations should happen, except that with ARC you have less programmer work, and chances to get it right are better.
You have two choices: Either turn ARC off for individual files. This is done in Xcode / target settings / Build phases / Compile sources by adding -fno-objc-arc to the build settings for individual files where you don't want to use ARC. If you use the same files in different projects, you have to do this in every target.
The other choice is to convert the files to ARC. Let the compiler run, remove offending memory management code, which is mostly retain / release / autorelease. If the code uses CoreFoundation functions, then you really need to understand memory management, just hope it doesn't. Use "Analyze" to let the compiler check very carefully that everything is fine.
I am trying to convert an old code to an ARC code.
However, i am getting a build error at the following line
[[token retain] autorelease];
I get 3 errors in the following order:
-'autorelease' is unavailable: not available in automatic reference counting mode
-[rewriter] it is not safe to remove an unused 'autorelease' message; its receiver may be destroyed immediately
-ARC forbids explicit message send of 'autorelease'
If i remove this particular line, then the code compiles correctly
If that is all that is on the line, you can probably just remove it. That code claims a reference to the object but also says you don't want to worry about releasing later, but with ARC you don't have to worry about it.
I am guessing that Xcode did not get rid of it automatically because of lack of context. If it had been in a more common location, such as in a return statement, it would be obvious what the intent was. When it is all by itself, it could be, but probably is not, something more complicated.
ARC manages your memory for you, so you don't need to call "autorelease", "release", "retain" etc. With ARC the compiler retain and release objects as necessary for you so you don't have to explicitly make these calls. If you want to manually manage your memory disable ARC, or you can use the compiler flag "-fno-objc-arc" to disable ARC on a specific class.
ARC means you don't have to use release, retain or those other pesky memory management things. ARC add them all for you automatically when you compile the app. Read more here
If you have old code where it would not be the best solution to remove all the memory management calls, then check this answer to disable ARC for particular files
my app is developed with ARC disabled from the beginning, now i decided to take advantage of ARC techniques, when i try to convert the project to ARC i keep getting errors wherever release autorelease methods are exist, does that mean i have to dig into my project and get rid of any methods related to memory management? thanks
Yes, you are not allowed to use release, retain, or autorelease in ARC code. If it's too much of a hassle, you can disable ARC on a per-file basis as described here: How can I disable ARC for a single file in a project?
There are a lot of good references on the web that deal with automatic reference counting, e.g.
http://www.raywenderlich.com/5677/beginning-arc-in-ios-5-part-1
or
http://www.mikeash.com/pyblog/friday-qa-2011-09-30-automatic-reference-counting.html
I want to transition my App to ARC. I can change Objective-C Automatic Reference Counting to YES but that does not automatically remove releases retains etc.
The Transitioning to ARC Release Notes states:
Xcode has a new tool that automates the mechanical parts of the ARC conversion (such as removing retain and release calls) and helps you to fix issues the migrator can’t handle automatically. The migration tool converts all files in a project to use ARC. You can also choose to use ARC on a per-file basis if it’s more convenient for you to use manual reference counting for some files.
How do I invoke this tool in Xcode?
Oh man I just found it:
Convert > To Objective-C ARC
I checked in Xcode's help first where I could not find it.
When trying to use -retain, -release, and -dealloc while building my application using automatic reference counting in Xcode 4.2, I get an error like the following:
Automatic Reference Counting forbids
explicit message send of 'dealloc'
Why am I seeing this error? Are -retain, -release, and -dealloc no longer allowed under automatic reference counting?
Basically:
When using ARC, it's all or nothing. Either the compiler is managing all of the retains/releases/deallocs for you, or it is doing nothing. You cannot intersperse your own calls to them, because the compiler wants to do it all itself. It can make absurd optimizations by doing this (for example, a method that returned an autoreleased object under Manual Memory Management may now produce an object that never ends up in an autorelease pool). If you were to start sprinkling in your own calls to retain and release, then the compiler would have to work with these and wouldn't be able to perform a lot of the optimizations that it wants (and that you should want).
And as an added bonus, invoking -retainCount is now a compiler error! OH HAPPY DAY!
in response to AliSoftware: we CNA mix ARTC and not-ARC frameworks, and also arc and not-ARC source.
(I did it..)
The basic ideas are:
1) compiler will insert/remove calls as a very-very-good cocoa programmer can do
2) cocoa is ANYWAY C code, so we have separate compilations, so the linker CAN link binaries produced by multiple sources. Think it as we can mix asm and cocoa, or C and pascal...
in main opinion the Appleadvantege over c# / java is here: we are alway allows to mix, and, using a COMPILER technique 8non a runtime..) we can rush performance beyond.
Under automatic reference counting, retain, release, and dealloc are not allowed.
If you have an existing code, you can keep using it as is with the -fno-objc-arc you can selectively disable ARC on any file.
If you want to disable ARC on MULTIPLE files:
Select desired files at Target/Build Phases/Compile Sources in Xcode
PRESS ENTER. (double click selects only one file)
Type -fno-objc-arc
Press Enter or Done
As I have pointed out in my answer on Xcode ARC, you can compile specific source files as non-ARC. Dave DeLong's answer is a bit off. It doesn't include the fact that you can instruct the compiler to compile source as non-ARC in an ARC-enabled project (as explained here).